Liquid chromatographs have a passage-switching valve for changing the passage according to the purpose, such as selecting a sample solution to be injected into a mobile phase or introducing a cleaning liquid for washing a column. A typical example of the channel-switching valve used in a liquid chromatograph is a rotary valve consisting of a stator having a plurality of ports (openings) individually connected to different passages and a rotor having a passage groove, where the rotor, while being strongly pressed against the stator, can be rotated and slid so as to connect the openings in the stator (Patent Literature 1).
In such a rotary passage-switching valve, in order to prevent a leakage of liquid between the stator and the rotor, a hard material (e.g. a metallic or ceramic material) is used for the stator, while a material (e.g. resin) softer than the stator is used for the rotor to improve the degree of contact with the stator. Furthermore, a high level of contact pressure (e.g. 50 MPa or higher) is applied to the sliding surfaces of the two elements.